This invention relates to a process for the co-production of dicarboxylates and acids.
U.S. Pat. No. 3,579,566 discloses that the hydrogenation of a carboxylic acid anhydride to give an alkylidene dicarboxylate plus an acid may be carried out using a catalyst comprising a complex of a Group VIII noble metal with a trihydrocarbyl phosphine, stilbine or arsine. However, the reaction products obtained by this process are complex mixtures, and the yield of the desired dicarboxylate is very low. In particular, the carboxylic acid which, according to the stoichiometry of the reaction should be formed in a quantity equimolar with the dicarboxylate, is formed in large excess. Thus, in Example 1 of the specification, the molar ratio of acetic acid to ethylidene diacetate is 6.7:1. Further, the temperatures and pressures required for the reaction are very high.
It has now been found that by the use of a specific catalyst-promoter system in the reaction of hydrogen with a carboxylic acid anhydride, the process can be carried out giving good yield and high selectivity to the desired products.